TRICHOMONAS-VAGINALIS - ULTRASTRUCTURAL BASES OF THE CYTOPATHIC EFFECT

The in vitro cytopathic effect of Trichomonas vaginalis on epithelial cells was explored through the interaction of trophozoites of the viru lent strain GT-10 with MDCK monolayers. The interaction was analyzed t hrough electrophysiology, video microscopy, and transmission and scann ing electron microscopy. Electrical measurements revealed that living parasites produced severe damage to the cell monolayers within 30 min, manifested as a rapid decrease in transepithelial resistance. Microsc opic observations demonstrated that when placed in contact with epithe lial cells, trichomonas formed clumps through interdigitations and tra nsient plasma membrane junctions between adjacent parasites. Also, att ached trophozoites adopted an ameboid shape. The in vitro cytopathic a ction of T. vaginalis on MDCK cells was initially evident by modificat ions of the plasma membrane, resulting in opening of tight junctions, membrane blebbing, and monolayer disruption. After 15 min of interacti on the damage was focal, concentrating at sites where parasite clumps adhered to the monolayer. At 30 min practically all MDCK cells were de ad, whether or not trichomonas were attached to them. These events wer e followed by detachment of lysed cells and complete disruption of the monolayer at 60 min. Electron microscopy demonstrated a peculiar form of adhesion that appears to be specific for trichomonas, in which the basal surface of T. vaginalis formed slender channels through which m icrovilli and cytoplasmic fragments of epithelial cells were internali zed. The same sequence of lytic events was found with the less virulen t GT-3 strain. However, the time course of cytolysis with GT-3 parasit es was much slower, and lysis was limited to areas of attachment of T. vaginalis.